One of the early and best tools I bought when I got my house was a Makita cordless drill. I bought it as part of a combo pack that also included a cordless circular saw with a 3 and 5/8″ blade. That blade is too small to cut a 2×4, but is enough to cut through plywood, siding, and 1×4’s. I used it to cut siding for the garage and the back of my house. I use it sometimes when I have a bunch of limbs that I am trying to cut down to 4′ lengths, working very well on the tangle of limbs that is privet. But the batteries are really old now and don’t hold a charge for more than a few minutes. New batteries are very expensive: at least $50 for one. The nice thing is they have NiMH batteries with more capacity than the NiCad one I have, but those are about $70. This is kind of similar to my problem with VersaPak tools that I bought at about the same time, actually. I wound up paying extra for NiMH.
Cordless tools nowadays have a lot more power, often 18 volts instead of the wimpy 12 volts of my tools. And with higher voltage you can get more substantial circular saws that will cut a 2×4. But those aren’t cheap either. Combo packs today seem to include a cordless drill and an “impact driver,” which looks like another cordless drill to me.
In its day, the Makita was top of the line. I saw a picture of a drill just like mine being used on the space station one time. I’m not sure Makita leads the field anymore though. I’m not sure who does. I thought about possibly cracking open a battery pack and adding new cells. For a 12V pack, there are 10 1.2V “sub C” size cells in series to give 12V (14.4V would be 12 cells), but if I could do that, somebody else was probably already offering rebuilt battery packs. I found some generic replacement packs with NiMH cells on eBay from a reputable seller (imax_expert, 78,890 items sold and 99.9% positive feedback) that cost about $30. The only problem is that my Makita charger doesn’t support NiMH cells, but I like that the NiMH is more environmentally friendly (no cadmium) and has 3.0 amp-hours of capacity instead of 2 that my NiCad batteries originally had. To avoid overcharging my Versapak cells, I have been using my hobby charger, which can charge just about any kind of battery pack, but it still seems to get the cells pretty hot, so I don’t trust it completely. I wound up getting a temperature sensor for the hobby charger, but I don’t know where it is now despite a lot of searching. I don’t know that it would matter with the Makita battery pack since it is encased in plastic and the temperature sensor might not work correctly.
Anyway, I could get two batteries (the combo pack originally came with two batteries, which is nice because you can be charging one while you use the other), but there isn’t much of a discount, so I figured I would just buy one and make do. I can always buy another one if I need to.
I got the battery today, which was amazingly fast for delivery from California. The battery was charged to about 12V, so I think it was mostly charged. I hooked it up briefly to my charger which seemed to be happily applying charge up to 13V before I had to go to work. For AA batteries, those typically charge up to 1.45V or so before cutting off, so this pack might charge up to 14.5V. It also fit the drill perfectly, so that was no problem. Hopefully this weekend, I can put it through its paces.
After charging the battery up over 14 volts, I wanted to do a discharge cycle to measure the capacity and see if it is really 3000 mAh. I found some sub C size NiMH batteries with capacity of 4200 mAh, so I was hoping I would get even higher capacity than 3000. However, I just stopped the charging at about 14.5V, not a true termination, since I didn’t want the batteries getting hot. I set the hobby charger to discharge at 1 amp, which is its maximum setting, so it should take about 3 hours. However at this voltage level, it can’t even discharge at 1 amp, so instead it was 0.4 amps most of the time and 0.5 amps towards the end as the voltage went down. This is a lot less than the drill or saw actually draw, so it isn’t that realistic, but it’s the best I can do. The charger won’t discharge for longer than 160 minutes, so it timed out a couple of times, plus I didn’t want it running when I wasn’t home or was asleep. So over 3 sessions, it saw a total capacity of 2,619 mAh over about 6 hours (at a more realistic draw with a higher current, it would have less capacity). That’s not 3,000 mAh, but it is a lot more than 2,000, and the battery wasn’t all the way full. I charged the battery again at 1.5 amps and put over 3000 mAh (I didn’t write down the exact number) in it this time, so I think the capacity is probably right around 3000 (you don’t get out quite what you put in). After running it down again, I got 2,946 mAh, so I think it is as advertised.